1. Field of the Invention
The present invention relates to an audio output device connectable with a plurality of devices and a method for controlling the same.
2. Description of the Related Art
An image and audio playback system may include a playback device such as a video camera or recorder, an audio output device such as a television device having an internal speaker, and an audio system such as an AV amplifier having an external speaker. In recent years, an interface termed a HDMI (High-Definition Multimedia Interface) has been used in which these devices are connected with a single cable to enable transmission of image data, audio data or control data. HDMI has the advantage that a user can avoid a troublesome operation of connecting a plurality of cables such as image cables and audio cables since devices can be connected using a single cable. The popularity of HDMI-compliant goods has resulted in an increase in television devices provided with a plurality of HDMI terminals.
HDMI uses three transfer lines including a transition minimized differential signaling (TMDS) line, consumer electronics control (CEC) line and a display data channel (DDC) line. The TMDS line transmits image data, audio data and additional data. The CEC line transmits control data (CEC commands) for controlling connected equipment. Communication using CEC commands enables controlling among connected equipments.
The DDC line transmits data tables termed extended display identification data (EDID). The DDC line is also used in confirmation processes for copyright protection processes termed high-bandwidth digital content protection (HDCP). For example, a video camera acquires an EDID stored in an AV amplifier or television device for connection, confirms the equipment capability (audio output performance or image display performance) and outputs audio data or image data corresponding to those capacities.
A television device provided with a plurality of HDMI ports (HDMI connection terminals) will be considered. When a plurality of EDID-ROMs is provided corresponding to a plurality of HDMI ports, if a video camera is connected to any one of those HDMI ports, equipment performance information (audio output performance information or image display performance information) of the television device can be acquired from the corresponding EDID-ROM.
However, the connection arrangement of equipment or the power supply state of the equipment sometimes may not allow a video camera to output audio data or image data as playback content in a suitable format.
For example, when a video camera (playback device), AV amplifier (audio system) and television device (audio output device) are connected in series, the video camera may not be able to access the EDID-ROM of the television device in a case where the power supply of the AV amplifier is OFF. As a result, since the video camera cannot confirm the equipment performance of the television device (audio output performance or image display performance), the problem arises that audio data and image data cannot be output in a suitable format.
Japanese Patent Application Laid-Open No. 2007-124469 discusses a system in which source equipment, an AV amplifier and a television are connected in series. In this system, even when the AV amplifier is in a power standby mode, it is possible to watch the playback content of the source equipment. According to the system, the AV amplifier is provided with a data table (EDID) indicating a signal playback performance to the source equipment. While the AV amplifier is ON, data is stored in the data table indicating the signal playback performance of the AV amplifier. When the AV amplifier is OFF, data indicating the signal playback performance of the television is rewritten in the data table, which is equivalent to a state in which the source equipment and the television are directly connected.
Japanese Patent Application Laid-Open No. 2007-179707 discusses a system in which a DVD player, AV amplifier and TV are connected in series and discusses a technique of power supply control for respective equipment according to the format of the playback content. More precisely, the DVD player determines the presence or the absence of an audio signal and image signal of the playback content as well as the format. When the playback content is only an image signal, the TV power supply is controlled to be ON and when the playback content is only an audio signal, the AV amplifier is controlled to be ON. Furthermore when the playback content includes both an image signal and an audio signal and the audio format is 5.1 ch, the power supply of both the TV and the AV amplifier are controlled to be ON to enable audio output from the AV amplifier and image display by the TV.
On the other hand, an arrangement is considered in which an AV amplifier (audio system) is connected to one HDMI port of a television device (audio output device) and a video camera (playback device) is connected to another HDMI port (hereafter “parallel connection”). In this case, the video camera can access the EDID-ROM of the television device. As a result, when video camera confirms the audio output performance of 2 ch of the television device, even when the audio format of the playback content is 5.1 ch, audio data downmixed into 2 ch is output. Thus, even in the event that the AV amplifier has a 5.1 ch audio output performance, the audio output performance of the AV amplifier is not effectively utilized and a sufficient audio effect for the playback content is not obtained.
Thus, the problem arises that, in view of the format of the playback content, a user must correctly determine whether the playback device, the audio system and the audio output device are to be connected in series or whether the audio system and the playback device are to be connected in parallel to the audio output device. When a suitable connection arrangement is not realized, audio data as the playback content is not output in a suitable format and a sufficient audio effect for the playback content is not obtained.
Therefore, when the connection arrangement of the playback device, the audio system and the audio output device is not suitable, the audio data as the playback content is not output in a suitable format and a sufficient audio effect for the playback content has not been obtained.
The techniques discussed in Japanese Patent Application Laid-Open No. 2007-124469 and Japanese Patent Application Laid-Open No. 2007-179707 are premised on serial connection of the playback device, audio system and audio output device and do not consider other connection arrangements. For example, an arrangement in which the audio system and the playback device are connected in parallel to the audio output device is not considered.